1. Field of the Invention
This invention relates to sand guards for preventing the excavated face of land from collapsing and sliding and, more particularly, is concerned with an expansion beam for shoring up such sand guards.
2. Description of the Prior Art
As a beam which is utilized for shoring up sand guards, in recent years there has been used a certain kind of expansion beam. This expansion beam is chiefly made up of a piston and cylinder-type expansion device which is put into action by the aid of hydraulic liquid, is able to expand and contract, has a pair of pads attached to both ends of the expansion device, also has a plug which is attached to one of the pads, and is used for pouring the hydraulic liquid into the expansion device.
The plug is one which has within itself a non-return valve. To this plug there is connected detachably a socket of a hose extending from a pump, whereby the hydraulic liquid is poured into the expansion device until reaching a prescribed pressure. After the socket is separated from the plug, then the non-return valve functions in such a manner that the hydraulic liquid is unable to flow out from the expansion device.
However, the plug is easily damaged or broken off due to falling rock and the like while in use because of its part projecting over the pad, wherefore the non-return valve sometimes does not properly work or sometimes malfunctions with the breakage of the plug. Thus, the liquid flows out from the expansion device and the pressure therein is reduced, with the result that the expansion beam can not fulfill the function of shoring up sand guards.
The present invention is so designed that the hydraulic liquid does not flow out from the expansion device even when the plug is damaged or broken.